The research proposed herein aims to elucidate a novel inhibitory pathway against human immunodeficiency virus type 1 (HIV-1) infection. We hypothesize that a sulfotyrosine binding site of the envelope glycoprotein 120 (gp120) can be exploited to prevent binding to the (3 chemokine receptor CCR5, and potentially other chemokine receptors, which is requisite for viral entry. As yet there are no inhibitors known to target this receptor. Given the highly adaptive response of HIV-1to immune and therapeutic challenges, the most effective clinical approaches rely upon multi-drug cocktails targeting multiple stages of infection and viral reproduction. Adding to the menu of available targets addresses a key challenge in HIV chemotherapy. Toward this goal we set three specific aims. The first is to clarify the roles of the two essential sulfotyrosine residues (TyslO and Tys14) in the CCR5 N terminus using conformationally constrained helical N terminal sulfopeptides. The second aim is to elucidate the auxiliary interactions involved in binding to the sulfotyrosine binding site on gp120 using template constrained cyclic peptide viral entry inhibitors. The final aim is to develop structure activity relationships (SARs) for small molecule targeting the HIV entry pathway identified by high throughput screening. These goals will be approached using a combination of molecular design, chemical synthesis, computational modeling, high throughput screening, and biological assays. Taken together these three aims elucidate a new inhibitory pathway against HIV-1 infection. Continually rising numbers of HIV infections and the recent success of viral fusion inhibitors in the clinical treatment of HIV stress the need to identify and exploit additional viral entry inhibitors. While structural components involved in the CD4-activated binding of gp120 to cell surface co receptors have been recognized for several years, clear evidence of a sulfotyrosine binding site on gp120 has only recently been presented. At present there are no known inhibitors targeting gp120's role in co receptor binding. These recent findings raise significant questions. Can we exploit the sulfotyrosine binding site on gp120 to suppress viral entry? How general is the role of the sulfotyrosine binding site in mediating viral entry among various viral phenotypes? PUBLIC HEALTH RELEVANCE: Answering these questions provides both a fundamental understanding of the mechanism of HIV-1entry and uncovers new tools with which to impair HIV infections.